The present invention relates to a microwave electrodeless discharge lamp apparatus in which microwaves oscillated by a magnetron excite luminescent materials to lead to discharge emission.
Hitherto, this type of microwave electrodeless discharge lamp apparatus is disclosed in, for example, a publication of JP56-126250 A.
Namely, as shown in FIG. 5, a conventional apparatus includes a magnetron 14 generating microwaves, a cylindrical hollow container 2 made of metal mesh materials that cannot transmit microwaves but can transmit a light, a waveguide 15 propagating the generated microwaves to the hollow container 2, a container 16 housing the magnetron 14 and the hollow container 2.
The magnetron 14 is provided with an antenna 10 oscillating microwaves, a magnetron tube 17 substantially generating microwaves, a yoke 9 forming a magnetic path in such a manner that surrounds the magnetron tube 17 and a radiation fin 18 radiating heat that was generated at the magnetron tube 17. The hollow container 2 includes an electrodeless discharge tube 5 that is supported and fixed by a supporting stick 4 made of silica glass and that is filled with luminescent materials. On a part of the wall of the container 16, a cooling fan 19 is provided so as to cool the magnetron 14.
Next, an operation of such a conventional microwave electrodeless discharge lamp apparatus will be explained.
Microwaves generated at the magnetron tube 17 are oscillated from the antenna 10 into the waveguide 15, propagated inside the waveguide 15 and fed into the hollow container 2 by way of a feeding hole 11 of the waveguide 15. The fed microwaves excite the luminescent materials sealed in the electrodeless discharge tube 5 to lead to discharge emission. When the magnetron 14 generates the microwaves, heat loss occurs in the magnetron tube 17, thus raising the temperature of the magnetron tube 17. As a result, an unstable operation or short lifetime of the magnetron 14 is caused. Therefore, in order to control the temperature of the magnetron tube 17 to such a temperature that does not affect the practical use of the application, the cooling fan 19 is operated to feed cooled air into the yoke 9 at about 1000 liter/min. Thus, a forced cooling of the magnetron tube 17 is carried out. Thereafter, the cooled air flows out from the apparatus by way of a ventilating hole 20, the feeding hole 11 and the container 2.
However, since such a conventional microwave electrodeless discharge lamp apparatus uses a forced cooling system using a fan, the apparatus is susceptible to the influence of the operation environment. There was a problem in that, for example, suction or accumulation of dust, dirt, insect, etc. by the apparatus may cause the deterioration of the magnetron tube or the cooling fan, etc. Consequently, the long lifetime of the apparatus cannot be realized.
Furthermore, there was another problem in that great noise occurs due to the rotation of the fan and air stream.
It is therefore an object of the present invention to provide a long lifetime microwave electrodeless discharge lamp apparatus capable of inhibiting the generation of noise.
In order to achieve the above-mentioned object, the microwave electrodeless discharge lamp apparatus of the present invention includes a magnetron having a magnetron tube and a yoke that surrounds the magnetron tube, a container housing at least the magnetron tube, a propagation path in which microwaves oscillated by the magnetron are propagated, an electrodeless discharge tube sealing luminescent materials excited by the microwaves to emit light, wherein a space defined by the yoke is communicated with the inside of the container, and wherein a fluid is sealed in the container.
According to such a microwave electrodeless discharge lamp apparatus, heat generated in the magnetron tube is conducted in the fluid and the container and then radiated outside. Thus, the magnetron tube can stably be operated. Furthermore, the magnetron, etc. can be protected from the contamination of foreign substances causing the deterioration of the magnetron tube, etc. In addition, since the fluid circulation uses the thermal convection, a cooling of the magnetron tube can quietly be carried out.
It is preferable in the above-mentioned microwave electrodeless discharge lamp apparatus that the container is formed of good thermal conductors. With such a microwave electrodeless discharge lamp apparatus, heat of the fluids are easily radiated to the outside via the container.
Furthermore, it is preferable that the container is provided with a circulation path in which the fluid circulates.
Furthermore, it is preferable that the circulation path is formed by making the container a double wall structure. With such a microwave electrodeless discharge lamp apparatus, since the surface area of the container can be increased, the amount of the radiated heat from the fluid is increased, thus enabling the cooling efficiency of the magnetron tube to be improved.
Furthermore, it is preferable that the container is provided with a radiator radiating heat from the fluid. With such a microwave electrodeless discharge lamp apparatus, the amount of the radiated heat from the fluid is increased, thus further improving the cooling efficiency of the magnetron tube. Furthermore, the amount of fluid to be sealed can be reduced, which can lead to cost reduction, miniaturization and weight reduction of the apparatus.
Furthermore, it is preferable that the radiator is a conduit provided with a large number of radiation boards on its outer surface.
Furthermore, it is preferable that the radiator is formed of a plurality of thin conduits arranged in parallel. With such a microwave electrodeless discharge lamp apparatus, since the surface area of the container can be increased, the amount of the radiated heat from the fluid can be increased.
Furthermore, it is preferable that the fluid is insulating oil. Such a microwave electrodeless discharge lamp apparatus have excellent electric insulating property, fluidity, cold fluidity and metallic corrosion behavior or the like.